1. Field of The Invention
The present invention relates to a method which pertains to the separation of pulp that contains magnetic constituents in a wet-magnetic, low-intensity separator of he concurrent kind, in which a cylindrical, horizontally mounted rotatable drum coacts with non-rotating magnets disposed in said drum in a manner to convey magnetic constituents in contact with the drum surface to a magnetic concentrate outlet, and in which method pulp which is depleted of magnetic constituents is separated as waste at a region remote from the concentrate outlet in a direction opposite to the direction of drum rotation.
The invention also relates to a wet-magnetic separator for carrying out the method.
2. Description of the Related Art
The magnetic separation of ores is an old technique in the art. Such methods include both wet-magnetic and dry-magnetic processes. With regard to the strength of the magnetic fields, it is possible to divide the wet-magnetic processes into low intensity processes, WLIMS (Wet Low Intensity Magnetic Separation) and high intensity methods, HGMF (High Gradient Magnetic Field). There is also an intermediate process DMHG (Dense Media High Gradient) in respect of extremely fine material of low magnetic concentration, such as tailings derived from flotation enrichment processes for instance. All of the magnetic separators and separation processes known hitherto are found described in general textbooks available in the field of mineral dressing, and in brochures produced by apparatus manufacturers, such as Sala International for instance.
Of all of the magnetic separation methods known at present, the wet-magnetic low intensity separation method is the one most generally used, whereas the other methods are of a more particular kind, for instance intended for application with suspensions having low concentrations of magnetic material or containing only weakly magnetic or paramagnetic material, or intended for dry ground material.
The wet-magnetic, low intensity methods are effected in a rotating drum in which there is stationarily mounted a magnetic yoke which is comprised either of permanent magnets or of electromagnets and which is lowered partially into a tank containing the pulp slurry. As the drum rotates, the magnetic yoke generates in the tank a magnetic field which is effective in transporting magnetic constituents of slurried ore (pulp) or the like fed to the tank from one side of the tank to the other, while non-magnetic constituents are removed from the tank somewhere therebetween. The whole of the upper part of the drum, i.e. that part which does not extend down into the tank, is thus not used in the separation process. The pulp level in the tank is normally about 25-50 mm above the lowest part of the drum. In the case of dry magnetic separation processes effected in a so called Mortsell separator using a drum enclosed in a chamber, the upper part of the drum is also used in the separation process, since the dry material to be separated is delivered close to the highest point of the drum, the magnetic material being separated close to the lowest point of the drum. A separator of this kind is described, for instance, in DE-C-750727 and functions to separate iron filings and chips from waste sand, wherein adhering concentrate is removed from the drum by spraying with water.
The separation result is influenced by several factors. in this case, by separation result is meant the yields of magnetic material in the concentrate extracted or the concentration of non-magnetic material in the magnetic concentrate. The most important of these factors is the strength and configuration of the magnetic field, the type of tank used, the diameter of the drum and the speed at which the drum is rotated.
The magnetic field is normally divided into several zones, for instance a pick-up zone, a transport zone and a dewatering zone, and extends from 110.degree. to 120.degree. around the drum circumference. A magnetic field of about 500-1000 gauss is suitable for the separation of magnetite.
The separation result is also influenced by the diameter of the drum, wherein a larger diameter tends to provide higher yields and greater capacity. Normal drum sizes range from 600 mm to 1200 mm.
One known method of improving the separation result includes a washing stage in which water is delivered adjacent the concentrate outlet and the water is allowed to flow into contact with the concentrate on the drum surface over a shorter or longer path. Such methods are described, for instance, in SE-C-38777 and U.S. Pat. No. 2,945,590. Publications SE-C-198980 and SE-C-227295 describe similar methods, although in this case the washing stage is placed above the concentrate outlet. U.S. Pat. No. 2,698,685 describes another method, in which water is delivered in the form of jets which function to form a type of barrier through which non-magnetic material is prevented from passing. The effect produced is similar to the effects produced by the aforesaid washing methods.
The types of tanks used are concurrent tanks, countercurrent tanks and counter-rotation tanks. Countercurrent, or contraflow, is often more effective than concurrent, but does not enable large particles (&gt;0.8 mm) to be handled effectively, whereas the concurrent technique is able to handle particle sizes of up to 6 mm. Counter-rotational separators are suitable for applications where yield is more important than quality.
All of the result-influencing factors known at present, however, have natural limitations and despite the application of optimally chosen parameters, optimal separators and careful trimming of the apparatus used, the yields obtained or the concentrations of desired materials in the products are far from being complete. For example, the wet-magnetic separators are often used in multi-stage systems in which several separator drums are arranged in series. In this case, the separation result is a function of the number of series connected drums.